1. Field of the Invention
The present invention relates to a valve timing controller that varies the opening and closing timing of intake and exhaust valves according to an operation condition of an engine.
2. Description of Related Art
An automobile or motorcycle may be equipped with a valve timing controller that varies the opening and closing timing of intake and exhaust valves according to an operation condition of an engine, such as revolution speed (for example, see JP-A-2005-54590).
With reference to FIG. 11, the period from an engine start time ‘a’ to a control start condition acquisition time ‘b’ corresponds to a stand-by period t for an initialization process. During the stand-by period t, a control target value A varies according to the operation condition of the engine. The difference between control target value A and the actual spark advance value is large at control start condition acquisition time b. When the actual spark advance value is shifted to a value equivalent to target value A in a short time, a spark advance update speed B1 (spark advance amount per unit time) becomes excessively high. Such a rapid increase in engine output may have an adverse effect on drivability such as a feeling of jumping out of the vehicle. This adverse effect is more serious for lightweight and small-sized vehicles such as motorcycles than for larger vehicles such as automobiles.
In order to minimize this effect, as shown in FIG. 12, one possible solution is to use a lower spark advance update speed value B2 to reach control target value A after control start condition acquisition time b. However, when a low value is set as the spark advance update speed at the control start condition acquisition time, a longer time is required until the spark advance value becomes the control target value, even when the driver or rider widens the throttle opening after the control start condition acquisition time. Thus, engine output does not sufficiently increase when the driver or rider desires to accelerate the vehicle and a rapid increase in engine output cannot be achieved.